A motor grader is a versatile apparatus for road work, ditch work, site preparation and other surface contouring and finishing tasks. A significant amount of a motor grader's versatility is provided by its multiple course setting and course change options. In particular, a motor grader typically includes a steering function implemented via steerable ground engaging wheels while also allowing some degree of course correction or steering via lateral arching or articulation of the machine frame. In this manner, for example, a motor grader may be steered and articulated to follow a curve without driving the rear wheels across the area inside the curve.
Another type of operating mode made possible by the motor grader's multiple course setting options is sometimes referred to as “crab steer” or the “crab” position. Crab steer, or the crab position, is a mode in which the front and rear wheel sets are not inline but are nonetheless parallel with one another. In this position, the motor grader moves along a line that is nonparallel to the machine axis.
The possible reasons for operating the motor grader in this position are many. For example, crab steering allows the motor grader to grade a stretch of roadway without driving the machine's rear wheels over just-graded roadway portions. Thus for example, the machine front wheels may be on the roadway while the rear wheels may be off the roadway entirely, and the machine is nonetheless able to travel parallel to the roadway. Other benefits to operating in a crab steer mode include, for example, increased side slope stability, allowing off setting of tandems away from edge fill for safety or to prevent road shoulder rutting, and allowing the operator to level truck-dumped material without running the front of the machine over the pile.
However, due to roadway curvature, slight machine perturbations, and so on, it can be difficult to maintain a crab steer mode for an extended period of time. In particular, maintaining accurate crab steer normally requires the operator to note any deviations, determine whether the noted deviation is due to a steering or articulation inaccuracy, and then make the necessary primary corrections and any necessary secondary corrections.
While there are certain automatic steering solutions described for use in motor graders, these solutions do not solve the problem of maintaining a crab position for an extended period of time. For example, U.S. Published Patent Application 20110035109 describes a system wherein machine articulation is automatically controlled based on machine steering. However, the system of the '109 application adjusts machine articulation to maintain tracking between the front and rear wheels of the machine. See '109 application at [0051].
The present disclosure is directed to a system and method that address one or more of the problems set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of this disclosure nor of the attached claims except to the extent expressly noted. Additionally, the inclusion of any problem or solution in this Background section is not an indication that the problem or solution represents known prior art except as otherwise expressly noted.